The invention claimed and disclosed herein pertains to environmental climate control systems, and particularly to heat pumps for commercial or residential use.
A common environmental conditioning system (i.e., a heating, ventilation and air-conditioning, or xe2x80x9cHVACxe2x80x9d system) is the heat pump. The heat pump essentially uses a refrigeration cycle to move heat energy from a first environment to a second environment. The system is called a xe2x80x9cheat pumpxe2x80x9d because the temperature of the first environment is lower than the temperature of the second environment, and so the natural direction of heat transfer would be from the second environment to the first environment The heat pump reverses this natural flow of heat by xe2x80x9cpumpingxe2x80x9d the heat energy from a colder, first environment to a warmer, second environment. So long as there is at least some energy in the first environment, and an appropriate heat transfer fluid is selected, it is possible to transfer heat against the natural direction of heat transfer. The advantage of using a heat pump is that it can consume less energy to perform the heat transfer process than would be used to directly heat the first environment For example, if electricity is used to operate a heat pump to heat a first space, and the alternative is to heat the space with an efficient electrical heater, then the heat pump will typically consume less energy than would be used to directly heat the space using the electrical heater. A heat pump can be an attractive source of heating and cooling an indoor environmental space where the outdoor temperature does not reach extreme lows in the winter, and where the cost of electrical energy (used to operate a compressor and a fan in the heat pump) is not too high. When the cost of electricity becomes very high, then heating with natural gas may be a more economical alternative. However, where natural gas is not available (for example, in a rural or a remote setting), then a heat pump can be an attractive source of environmental heating and cooling even where the cost of electricity is relatively high.
Heat pumps are typically configured to operate in one of two modes: a summer mode and a winter mode. (These modes are alternately, and respectively, known as xe2x80x9ccooling modexe2x80x9d and xe2x80x9cheating modexe2x80x9d.) In the winter mode, the heat pump moves energy from a source of energy to an indoor environment, such as a residence or a commercial building. In the summer mode, the heat pump moves energy from the indoor environment to another location. Many heat pumps are configured to be able to switch from one mode to the other. Thus, the heat pump can act to heat an indoor environment in the winter, and cool the same indoor environment in the summer. Known sources of energy that can be accessed by the heat pump for winter mode include solar heat, ground or earth heat, ambient air, water (such as a river), and waste heat. Waste heat is more common in an industrial environment where heat from commercial processes (such as incineration) can be accessed. If the heat pump is to be used in the summer mode, then the objective becomes locating a destination to which heat from the indoor environment can be transferred. Obviously, for winter mode it is preferable to locate a source of energy having a large amount of available energy, such as solar energy. For summer mode, it is preferable to identify a location to which the indoor heat can be pumped which is relatively cool and will thus accept a large amount of heat. If the heat pump is configured to be capable of switching between modes, then it is preferable to locate a source which can provide heat for the winter mode, yet accept heat in the summer mode. The most common source is to use the outside ambient (or atmospheric) air. In this case, the heat pump is known as an air-to-air heat pump, since it moves heat between the air in the indoor environment and the air in the outdoor atmosphere.
A basic schematic of a heat pump 5 is depicted in FIG. 1A, and the basic thermal cycle of the heat pump is depicted in FIGS. 1B and 1C. FIG. 1A actually depicts a refrigeration configuration, but it can be considered as one or the other modes of a heat pump, depending on whether the heat exchanger which is located in the indoor environment is acting as the condenser (heating mode), or an evaporator (cooling mode). The xe2x80x9cheat pumpxe2x80x9d 5 thus comprises a condenser 10 (between points (4) and (1)), an expansion valve 20 (between points (1) and (2)), an evaporator 30 (between points (2) and (3)), and a compressor 40 (between points (3) and (4)). A refrigerant in vapor form is passed through the condenser 20. Heat is extracted from the vapor, causing a temperature drop and a loss in enthalpy xe2x80x9chxe2x80x9d between points (4) and (1) (see FIGS. 1B and 1C). As the vapor is passed through the condenser 10, it condenses to a liquid. The liquid refrigerant is then passed through the expansion valve 20 where it is flashed to a vapor, lowering the temperature of the refrigerant (see FIG. 1B between points 1 and 2). The cooled, vaporized refrigerant is then passed through the evaporator 30 where heat in the form of enthalpy xe2x80x9chxe2x80x9d is added to the refrigerant (see FIG. 1C between points 2 and 3). Note that very little (or no) temperature rise in the refrigerant occurs as the refrigerant passes through the evaporator (see FIG. 1B between points 2 and 3). The refrigerant vapor then passes through the compressor 40, where heat in the form of sensible heat (indicated by a rise in temperature T, as indicated in FIG. 1B between points 3 and 4), as well as enthalpy (FIG. 1C, between points 3 and 4) is added to the refrigerant. The pressure of the refrigerant is also increased, providing a motive source to circulate the refrigerant through the system 5.
Turning to FIG. 1, a prior art air-to-air heat pump is depicted in a schematic diagram. The heat pump 100 is depicted as operating in the winter xe2x80x9cheatingxe2x80x9d mode. The heat pump uses a heat transfer fluid or refrigerant (not shown) which flows in the various fluid lines in order to transfer heat from an outdoor atmosphere xe2x80x9cAxe2x80x9d to an indoor environment xe2x80x9cExe2x80x9d. A common refrigerant used in such heat pumps is a refrigerant known as xe2x80x9cR-22xe2x80x9d. The refrigerant is selected to have a flash point above the coldest anticipated outdoor temperature so that the refrigerant will still flash from a liquid to a vapor and thus absorb heat, as will be explained below.
The heat pump 100 comprises an indoor unit 102 and an outdoor unit 104. The indoor unit is located in the environment to be heated (such as a residence or an office building), and the outdoor unit is typically located out of doors and has access to the outdoor atmosphere. The indoor unit 102 comprises an indoor heat exchanger 108 comprising a series of coils or passes of fluid line through which the refrigerant passes. The coils are exposed to air from the indoor environment which is forceably passed over the coils by a blower 110. If a fluid in the coils 108 is at a temperature higher than the temperature of the environment xe2x80x9cExe2x80x9d, then heat energy from the coils 108 will be transferred to the environment air. The indoor unit 102 can further comprise a secondary heat source such as electrical heating element 111 which can be used to augment the heat from the coils 108. In the heating mode depicted in FIG. 1, the exchanger 108 acts as a condenser such that the refrigerant enters the top of the exchanger 108 through line 106 as a vapor. As the environmental air is passed over the coils and heat is extracted from the refrigerant, the refrigerant condenses to a liquid and passes out of the bottom of the exchanger via the distributor 112. The liquid refrigerant then passes through the check valve 114 and into the line 120. Although a small amount of refrigerant may also pass through the TEV 116, the bulk of the liquid refrigerant will pass through the check valve 114.) The indoor unit is also provided with an indoor thermal expansion valve (xe2x80x9cTEVxe2x80x9d) 116 and a drier 118, which are used in the cooling cycle, as will be described below with respect to FIG. 2. The check valve 114 allows fluid to flow out of the exchanger 108 and into line 120, but does not allow fluid to pass from line 120 into the exchanger 108, other than through the TEV 116. That is, for fluid to flow from line 120 into the exchanger 108, it must pass through the thermal expansion valve 116. The general direction of flow of the refrigerant in the heat pump 100 during the heating cycle is depicted by flow arrows adjacent to the various fluid lines in the figure.
The liquid refrigerant passes from the line 120 into the outdoor unit 104. The liquid refrigerant then passes through a drier 122 where water can be removed from the refrigerant. The refrigerant then passes through the outdoor unit thermal expansion valve (or xe2x80x9cTEVxe2x80x9d) 124 and then into the distributor 126, where the refrigerant is distributed to two coils in the outdoor heat exchanger 130. Outdoor atmospheric air xe2x80x9cAxe2x80x9d is passed over the coils of the exchanger 130 by fan 132 which is driven by electrical motor 134.
A check valve 128, which is in parallel with TEV 124, prevents the refrigerant from bypassing the TEV 124 and flowing directly into the outdoor exchanger 130. (When the refrigerant circulates in the opposite direction, the outdoor check valve 128 allows fluid to flow from the outdoor exchanger 130 into line 120. Although a small amount of refrigerant may also pass through the TEV 124, the bulk of the liquid refrigerant will pass through the check valve 128.) For fluid to flow from line 120 into the exchanger 130, it must pass through the thermal expansion valve 124. The thermal expansion valve 124 causes a pressure drop between the fluid line 120 and the coils of the exchanger 130. This pressure drop causes the liquid refrigerant entering the TEV 124 to flash to a vapor. The vaporization process removes a substantial amount of energy from the refrigerant, causing it to drop to a temperature below the temperature of the atmospheric air xe2x80x9cAxe2x80x9d which is passed over the coils of the exchanger 130. Thus, the vapor refrigerant in the exchanger 130 can receive heat energy from the atmospheric air xe2x80x9cAxe2x80x9d, even though the temperature of the atmospheric air xe2x80x9cAxe2x80x9d is below the temperature of the indoor environment xe2x80x9cExe2x80x9d. Thus, in the heating cycle depicted in FIG. 1, the outdoor exchanger 130, in combination with TEV 124, becomes an evaporator. FIG. 1C shows that the heat input into the refrigerant in the evaporator 130 is input in the form of enthalpy xe2x80x9chxe2x80x9d (versus sensible heat, which would be indicated by a rise in temperature).
The vapor refrigerant passes from exchanger 130 via line 136, through a reversing valve 138. The reversing valve 138 can be used to reverse the direction of flow of the refrigerant in the heat pump 100. This is done to allow the heat pump 100 to act in both a heating mode and a cooling mode, as will be described further below. From the reversing valve 138 the refrigerant (still in vapor form) passes into an accumulator 140. The accumulator essentially allows only vapor refrigerant to pass out of the accumulator 140, and traps entrained liquid refrigerant. (Liquid refrigerant can be formed in passing from exchanger 130 to the accumulator 140 as a result of a drop in temperature). The vapor refrigerant passes out of the accumulator 140 and into the suction side 181 of a compressor 142. The compressor raises the pressure (and consequently, the temperature (see FIG. 1B between points 3 and 4)) of the vapor refrigerant, and also provides the motive force for the refrigerant to circulate through the heat pump 100. As can be seen, high-pressure vapor refrigerant is discharged from the compressor 142 into line 143, where it then passes into line 106 of the indoor unit, to repeat the process of heat extraction described above. The heat absorbed by the refrigerant in the outdoor exchanger 130 is thus transferred to the indoor unit 102, where it is extracted in the exchanger 108 and transferred to the indoor environment xe2x80x9cExe2x80x9d.
Turning to FIG. 2, the heat pump 100 of FIG. 1 is depicted in a cooling (or xe2x80x9csummerxe2x80x9d) mode. In this mode, rather than transferring heat from the atmospherexe2x80x9cAxe2x80x9d to the indoor environment xe2x80x9cExe2x80x9d, heat is transferred from the indoor environment xe2x80x9cExe2x80x9d to the outdoor atmosphere xe2x80x9cAxe2x80x9d to thus cool the environmental space xe2x80x9cExe2x80x9d. The primary difference between these two modes is facilitated by the reversing valve 138, which is depicted in a different position in FIG. 2 than is depicted in FIG. 1. This causes the refrigerant to circulate in the opposite direction in the heat pump, as indicated by the circulation arrows drawn next to the fluid lines. Note that the refrigerant now passes through the indoor TEV 116 (and not the check valve 114) on the indoor side, and on the outdoor side the refrigerant passes through the check valve 128, and not the outdoor TEV 124. ( Although a small amount of refrigerant may also pass through the TEV 124, the bulk of the liquid refrigerant will pass through the check valve 128.) Simply put, in the cooling mode the indoor heat exchanger 108 become the evaporator, and the outdoor exchange 130 becomes the condenser. Thus, a low pressure refrigerant, in vapor form, is compressed by the compressor 142, and experiences a rise in temperature (as well as pressure). The compressed refrigerant vapor is then passed (via the reversing valve 138) to the outdoor exchanger 130, where atmospheric air is passed over coils containing the refrigerant. The refrigerant is cooled by the flow of air over the coils, and condenses to a liquid. The liquid refrigerant then passes, via the outdoor check valve 128 and line 120, through the indoor expansion valve (TEV) 116, where it flashes to a vapor, and the enthalpy of the refrigerant drops. The refrigerant vapor then passes through the indoor exchanger 108, where air from the indoor environment is passed over the coils of the exchanger. Since the refrigerant in the coils of exchanger 108 is lower than the temperature of the air in the environment xe2x80x9cExe2x80x9d, the refrigerant absorbs heat from the indoor air, thus cooling the indoor air. The cooled refrigerant vapor then passes back to the compressor 142, where it is compressed and the cycle begins anew.
As mentioned previously, one of the drawbacks to using a heat pump is that in situations wherein the outdoor temperature can become extremely cold in the winter (such as in Alaska), there may be insufficient heat in the atmospheric air to justify the use of the heat pump. That is, more energy is used to operate the heat pump than would be used to heat the environmental space directly. Also, in the face of rising electrical energy costs, alternative methods of heating (such as by using natural gas) may become less expensive than using a heat pump.
Yet another problem with prior art heat pumps is that in the winter, when the heat pump is operated in a heating mode and thermal energy is extracted from the outdoor atmospheric air, the drop in temperature of the atmospheric air as it passes over the coils of the outdoor exchanger 130 can cause moisture in the atmospheric air to condense on the coils. If the temperature on the coils is below the freezing point (about 32xc2x0 F., or 0xc2x0 C.), then ice forms on the coils of the outdoor exchanger. This ice will reduce the efficiency of the outdoor exchanger (i.e., the ability to transfer heat from the atmospheric air to the refrigerant in the coils). One solution to this problem is to temporarily reverse the cycle of the heat pump, and essentially put the heat pump in the cooling mode of FIG. 2. In this case heat is transferred from the indoor environment to the outdoor exchanger 130, causing the ice on the coils 108 to melt. This is known as a defrost cycle of the heat pump. This has the obvious detriment that it results in a cooling of the very environmental space which is trying to be heated. An alternative solution is to temporality heat the coils of outdoor exchanger 130 using an electrical heating element. The obvious drawback here is the use of additional electrical energy.
What is needed then is a heat pump which achieves the benefits to be derived from similar prior art devices, but which avoids the shortcomings and detriments individually associated therewith.
The present invention provides for a heat pump comprising a compressor having a compressor inlet and a compressor outlet, an indoor heat exchanger and an outdoor heat exchanger, and an outdoor thermal expansion valve. The heat pump further includes an auxiliary heat exchanger. An auxiliary fluid line and an auxiliary fluid pump circulate an auxiliary heat transfer fluid through the auxiliary fluid line. The compressor outlet, the indoor heat exchanger, the outdoor thermal expansion valve, the auxiliary heat exchanger, the outdoor heat exchanger, and the compressor inlet can be placed in respective serial fluid communication to thereby circulate a refrigerant fluid through the heat pump. The auxiliary heat exchanger is configured to exchange heat between the refrigerant fluid and the auxiliary heat transfer fluid. The auxiliary fluid line is in thermal energy communication with a primary source of auxiliary or supplemental heat. Preferably, the primary source of auxiliary heat is a fluid contained within a septic tank. The primary source of heat can also be the earth. In this way, when the heat pump is operating in the heat mode, supplemental heat can be provided to elevate the saturated suction temperature of the refrigerant at the compressor inlet, thereby providing more energy to be transferred to an indoor environment.
In one variation the heat pump is provided with a reversing valve allowing the heat pump to operate in a cooling mode as well as a heat mode. In this case the heat pump further includes an indoor thermal expansion valve, an indoor check valve in parallel fluid arrangement with the indoor thermal expansion valve, and an outdoor check valve in parallel fluid arrangement with the outdoor thermal expansion valve. The reversing valve is in fluid communication with the compressor outlet, and can be moved between two positions. In the first position (the heating mode) the compressor outlet is directed to the indoor heat exchanger. This puts the compressor outlet, the indoor heat exchanger, the indoor check valve, the outdoor thermal expansion valve, the auxiliary heat exchanger, the outdoor heat exchanger, and the compressor inlet in respective serial fluid communication with one another. In the second position, the compressor outlet is directed to the outdoor heat exchanger. This puts the compressor outlet, the outdoor heat exchanger, the auxiliary heat exchanger, the outdoor check valve, the indoor thermal expansion valve, the indoor heat exchanger, and the compressor inlet in respective serial fluid communication with one another.
In yet another variation, when the heat pump includes the reversing valve, the auxiliary fluid line can be configured to be in further thermal energy communication with a secondary source of auxiliary heat, such as solar energy. The heat pump can then include a solar energy isolation valve which can isolate the auxiliary heat transfer fluid line from the solar energy. In this way, solar energy can be used to augment the heating cycle, but can be isolated from the heat pump system during the cooling cycle. Further, in the summer (i.e., when cooling of the indoor environment is desired) the septic tank may be at a temperature below the temperature of the atmospheric air, in which case the septic tank can also be used to augment the cooling cycle.
Another variation on the present invention allows for an improved defrost cycle over prior art heat pumps. When the heat pump includes the reversing valve, a three-way defrost valve can be disposed between the outdoor heat exchanger and the auxiliary heat exchanger. A defrost line is placed in fluid communication with the compressor inlet. The three-way defrost valve is selectable to a first position to place the auxiliary heat exchanger and the defrost line in fluid communication for a defrost cycle. The three-way defrost valve is also selectable to a second position to place the auxiliary heat exchanger and the outdoor heat exchanger in fluid communication for the normal heating cycle.
The present invention also provides for a heat pump which can use heat extracted from an environmental space by the heat pump to preheat water, such as water used in a residential hot water system. Not only is there an efficiency in preheating the water, but this also has the effect of lowering the temperature of the refrigerant, allowing the refrigerant to extract more heat from the indoor environmental space. In this variation the heat pump is provided with the reversing valve described above, as well as a water preheat heat exchanger configured to transfer heat between the auxiliary heat transfer fluid and water. The water preheat heat exchanger has a preheat exchanger inlet and a preheat exchanger outlet for the auxiliary heat transfer fluid. The heat pump is further provided with a three-way water preheat inlet valve disposed in the auxiliary fluid line and selectable to a first position to direct the auxiliary heat transfer fluid from the auxiliary heat exchanger to the preheat exchanger inlet. The three-way water preheat inlet valve is also selectable to a second position to direct the auxiliary heat transfer fluid from the auxiliary heat exchanger to the primary source of auxiliary heat. That is, in the first position the water preheat cycle is used. This typically corresponds to the cooling cycle of the heat pump, used in the summer. However, during the cooling cycle, the water preheat system is disengaged to avoid chilling of the water in the water preheat exchanger (and consequently, the refrigerant in the heat pump).
These and other aspects and embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein: